The present invention relates to an imaging apparatus having an electronic imaging device.
On the occasion of imaging with an electronic imaging device, telecentricity on the image side becomes important unlike imaging with a film. Telecentricity means that the principal ray of a pencil of light to each image point becomes almost parallel to the optical axis after being emitted from the final surface of an optical system. That is, it means that the principal ray of the pencil of light to each image point intersects with the image surface almost perpendicularly.
The reason why the telecentricity on the image side becomes important in the electronic imaging device is that oblique incident light is disadvantageously shaded by the aperture of the pixel since the aperture of each pixel of the electronic imaging device is located at a position slightly away from the photodetection portion, causing a reduction in fill factor.
In recent years, a method for increasing the fill factor than that on the actual photodetection surface by arranging a microlens array on the surface of the electronic imaging device is adopted.
A method for preventing the fill factor from being reduced even if the angle of incidence of the ray to the image surface is increased by scaling the microlens, i.e., by arranging the microlens in a position shifted from the position of each pixel in conformity to the angle of incidence of the ray is adopted. The scaling of the microlens can cope with up to an angle of incidence of about 25°.
For example, JP 2005-57024 A proposes a method for providing a flattening film on a plurality of microlenses corresponding to a plurality of photodetectors and suppressing the reduction in fill factor by shifting the positions of the plurality of microlenses from right above the corresponding photodiode toward a center portion as they are located apart from the center portion of the photodetection surface to end portions.
However, since the angle of incidence to the image surface of the ray differs depending on the focal distance, the angle of incidence of the ray to the image surface is disadvantageously changed by the zoom position in the zoom lens where the focal distance changes.
In general, an exit pupil position is located away from the image surface at a telephoto end, and the ray is incident on the photodetection surface almost perpendicularly. In contrast to this, the exit pupil position is located closer to the image surface at a wide angle end, and therefore, the ray of a maximum image height is incident at a large angle on the image surface.
Therefore, a difference in the angle of incidence of the ray of the maximum image height on the image surface between the telephoto end and the wide angle end is consequently increased, and this cannot be managed by the scaling of the microlens.
If the difference in the angle of incidence of the ray of the maximum image height on the image surface between the telephoto end and the wide angle end becomes large, a shift in an image formation position on an imaging device occurs between the telephoto end and the wide angle end, and this causes a blur and the like.
Therefore, it has conventionally been a problem of the zoom lens to bring the angle of incidence of the ray at the wide angle end, at which the exit pupil position is located near the image surface, incident on the image surface close to perpendicular to the surface.
Particularly in recent years, there is a demand for reducing the size of the lens, and it is indispensable to shorten the length of the entire lens. In contrast to this, the length of the entire lens is disadvantageously increased when the exit pupil is set away from the image surface in order to bring the angle of incidence of the ray at the wide angle end close to perpendicular. Therefore, it is more difficult to make the angle of incidence of the ray at the wide angle end perpendicular.